DEVELOPMENTS IN MANUFACTURE OF COPPER WIRE 205 



tension of from 9 pounds for No. 25 wire to 3 ounces for No. 42 wire. 

 Fig. 15 illustrates its operating range on wire sizes No. 30 to No. 42, 

 showing the gradual narrowing of the limits as the sizes decrease. A 

 larger machine used for drawing loop cable wire from No. 18 to No. 30 

 B. & S. gauges contains a similar mechanism. 



The use of this sensitive device and a clutch which would slip without 

 overheating as the spool filled, together with improvements in the wire 

 drawing compound and the shape and quality of the diamond dies 

 later described, permitted the drawing of wire at speeds ranging from 

 2000 to 3000 feet per minute. 



Wire Drawing Compound 



At low speeds it was discovered that the compound for lubricating 

 wire drawing dies required little attention but as the speeds were in- 

 creased the necessity for close analytical control was evident. The 

 compound consists of an emulsion of soap, tallow, and water, the per- 

 centage of the soap and tallow being varied depending upon the size 

 of wire and type ot machine on which it is used. 



Ic is important that the degree of emulsification ^ be carried far 

 enough to break the tallow into particles about one micron in diameter, 

 so that the material will stay in suspension in the water. If the tallow 

 content is increased beyond a certain point, it holds in suspension in the 

 solution a large amount of the copper dust which flakes off in a very fine 

 state during the wire drawing operation and this clogs the dies and 

 causes breakage during the wire drawing. Ordinarily this copper dust 

 settles out of the solution while in the large cooling tanks and a con- 

 siderable amount is salvaged in this manner. 



Effect of Drawing on Copper 



Tests were made to determine if the drawing of the smaller cable 

 and all magnet wire sizes ^ in Brown and Sharpe (A.W.G.) steps was 

 yielding the maximum reduction possible per die. These tests 

 showed it was feasible to make much heavier than A.W.G. reductions 

 at the first draft when annealed wire or soft copper rod was being 

 drawn. It also showed that the elongation ^ of the rod or annealed 

 wire was rapidly reduced to the drawing minimum after the first pass, 

 and remained at that point throughout the process. 



* "The Theory of Emulsions and Emulsifications," W. Clayton. 



* A.W.G. ("American Wire" or "Brown and Sharpe" gauge) reductions are not 

 used in converting the rod to line wire; these are generally specified in B.W.G. and 

 N.B.S. gauges. 



* See Figs. 16, 17, 18, and 19 showing the elongation of the rod or wire dropping to 

 about 13-^ per cent at the first die reduction and remaining practically constant. 



